Flexible membrane materials are commonly used in many products that are required to have water repellency. These are mainly products for outdoor use, including pneumatic membrane structures, tents, and radar domes. The membrane material for use in these products is usually composed of a fabric of any suitable fiber material as a reinforcing member, having a rubber or plastic coating layer provided on its surface. This coating material of rubber or plastic protects the fabric under various conditions and further functions to water-proof and air-proof the membrane material and to make it water repellent, so as to prevent it from absorbing water and from forming a water layer on its surface. If the water content of the membrane material increases and a water layer is formed on the surface, various problems arise. For example, in the case of the pneumatic membrane structures and tents, the weight of the membrane material increases, losing the advantage of light weight which is characteristic of membrane materials. In the case of the radar dome, wave transmittance will decrease.
In membrane material products especially required to have water repellency, therefore, it is known to employ press molding to make the surface of the membrane material very smooth. For products required to have a much higher water repellency, the surface of the membrane material must be extremely smooth even though it is composed of a material having a relatively high water repellency, and for this purpose it has been proposed to laminate a fluorinated resin film of high water repellency on the press-molded surface or provide a layer of the fluorinated resin on the press-molded surface as described in, for example, U.S. Pat. No. 4,346,139. It has also been proposed to use a fluorinated resin for the entire coating layer. However, these conventional membrane materials have certain disadvantages.
The fluorinated resin used has poor adhesive properties, and consequently it is difficult to form a composite structure in which a fluorinated resin film will not easily peel off. Even if a uniform layer or film of the fluorinated resin is provided, when the membrane material is bent, cracks or wrinkles will develop because of the characteristic low elongation and high modulus of such films.
Since a relatively large amount of expensive fluorinated resin must be used, production costs are high. Such membrane materials have poor workability, and it is difficult to produce a membrane material of large area and length by press molding. A high temperature furnace is needed for high-temperature processing fluorinated resin at temperatures of 300.degree. C. or higher. Because of this high temperature processing, the fabric material that is used must be limited, and fabrics made of organic fibers cannot be used.